Proximity fuze



Oct. 21,1958 I W.S.HINMAN,JR., ETAL 2,856,852

PROXIMITY FUZE Filed ma 30, 1944 6 Sheets-Sheet 1 ATTORNEY 2 'Oct. 21, 1958 w. s. HlNMAN, JR., ETAL 2,856,852

PROXIMITY FUZE 6 Sheets-Sheet 4 Filed May 30', 1944 INVENTORS ZILRBUR ill/NAM JR, BY Y DIAMOND ,Filed May 30; 1944 OSCILLATOR Oct. 21, 1958 w. Sa-HINMAN, JR., ETAL' PROXIMIT! FUZE 6 Sheets-Sheet 5 TTORNEY 4 W. S. HINMAN, JR; ETAL Oct. 21,1958

PROXIMITY FUZE 6 Sheets-Sheet 6 Filed May 30, 1944 FIG. 12.

Poinf of Explosion from Target 5A (wave /engflr)= 35ft.

Generator wave Response of Radio Fuze IZOpaIses/Sec- Response of Radio Fuze 300pu/ses/ec.

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HAR Y DIAMOND Pulse rate per Second ATTORNEY 2,856,852 Patented Oct. 21, 1958 United Sttes Patent 2,856,852 PROXIMITY FUZE Wilbur S. Hinman, Jr., Falls Church, Va., and Harry Diamond, Washington, D. C., assignors to the United States of America as represented by the Secretary of the Navy Application May 30, 1944, Serial No. 537,983

r 11 Claims. (11. 102-702 (Granted under Title 35, U. S. Code (1952), sec. 266) This invention relates generally to electrical radiation responsive devices and particularly to proximity fuzes for use with projectiles.

In firing an explosive projectile at a target, it is difficult to time the explosion so that it will occur at the most advantageous position with respect to the target. This is especially true when the target is moving at high speed, as in the case of an airplane.

It is an object, therefore, to provide a fuze that will cause the explosion of a projectile when it approaches Within effective range of an airplane or other target. In carrying out this purpose, we incorporate an ultra-shortwave radio transmitter in the fuze. A portion of the transmitted radiation, reflected from the airplane when the projectile carrying the fuze approaches sufliciently near to it, reacts upon a novel electrical circuit in the fuze to cause the projectile to explode near the aircraft to destroy In our device, use is made of the well-known phenomenon by which radio waves are reflected from an object in their path. The fuze includes the combination of a radio transmitter, a special radio receiver, an ampliof aircraft and for other purposes. The principle of operation of these devices could possibly be extended to radio fnzes but experimental evidence shows that the results Will not be comparable to those obtained by us. Some of these devices have depended upon standing electromagnetic wave patterns produced by interference between the radiated and reflected waves, the determinations being made by measurements or indications of intensity as the receiving device is moved through regions of high and low field intensity resulting from the standing waves. Such devices are not comparable in eflectiveness with our invention, due in part to the fact that they require extremely accurate control of frequency and also to the fact that our device is based upon broadly diflerent principles.

Other devices of this nature, broadly considered, depend upon two general methods of operation:

(1) A reaction oscillator is closely coupled to an antenna system so that part of the electromagnetic energy radiated is received by the antenna system after being reflected from a target and reacts upon the oscillator to change its frequency or amplitude. This change is then used to operate the device when the intensity of the reflected radiation reaches a suflici ent value.

(2) Changes in electrical circuits caused by proximity of an object without regard to rapid motion.

Devices 1) and (2) outlined above do not depend upon relative movement between the antenna system and the target or object. It is in part a requirement that a radio fuze as defined in this description, be operated, not by proximity alone, but shall require rapid relative motion.

. This requirement avoids any fine tolerance limits on perfier of particular characteristics and a detonator which is operated by means of an electronic relay which, in turn,

is controlled by the amplifier.

The operation of the fuze depends upon the rate of phase change of the reflected wave with respect to the transmitted wave as well as the amplitude of the reflected wave. The variation in phase and amplitude of the reflected wave is detected, in our device, appearing as electrical pulses varying in phase and amplitude in definite relation to the variation in relative phases and amplitudes of the transmitted and reflected waves. pulses may be nearly periodic in special cases, but in the general case the instantaneous phases and amplitudes of the pulse pattern are complicated functions of the relative motion of the projectile and target, of their shapes and of their relative orientations. In our device, the amplifier These circuit is 'specially designed so that periodicity of the;

pulses is not necessary to the correct timing of the electronic relay.

The operation of our device is not dependent upon close control of a predetermined carrier frequency or of the regularity and intensity of a predetermined standing Wave pattern, but upon the amplitude and the dynamic I change of the amplitude and average periodicity of the pulse pattern or of a portion of the pulse pattern.

Further, the amplifier for these pulses is so arranged that it will admit pulses of predetermined slope or rate of phase change but will reject pulses of substantially different slope, either higher or lower;

Our electrical circuit makes use of changes in amplitude and phase of electrical fluctuations in the antenna circuit, produced by interaction of the transmitted and reflected radiation, to operate the detonator through the agency of a relay.

Various inventors have disclosed devices employing radiated and reflected radiation for determining altitude formance and permits the use of broadly stable circuits which are inoperative except when there is relative movement between the fuze and target, within certain predetermined limits of distance and speed.

As contrasted to a purely frequency phenomenon, the 7 operation of our fuze is based upon the manner of the change of phase and amplitude of the signals with time. A certain predetermined behavior of phase and amplitude of signal results in firing of the fuze. This is especially true for projectiles fired toward aircraft. An adequate signal intensity alone however will not cause the fuze to detonate. There must be a concomitant special behavior of phase and it is in this relationship that one outstanding feature of novelty of our invention resides. Other devices have relied upon staticinterference intensity patterns, whereas in our invention there must be relative movement between the radio fuze and the target in order to produce proper dynamic phase and amplitude variations.

In carrying out our invention along the above principles, an important feature is the creation of a controlled directional sensitivity of the fuze so as 'to produce'the proper concomitant bevhavior of phase and amplitude as the projectile approaches the target. Thus, the projectile will be detonated in proper aspect to the target with the result that the fragments will strike the target. The fuze is least sensitive in the direction along the axis of the projectile so that if it is traveling directly toward a target it will not be detonated prematurely.

If the projectile path lies to one side of the target then the relative velocity of approach of the fuze with respect to the target will constantly decrease until it is zero as it passes the target. As a result of this change of relative velocity of approach the phase of the resultant signal will also continually change, the rate of change becoming continually less as the projectile approaches the target but the amplitude of the signal will of course constantly increase as the distances between the projectile and target is lessened. By means of a wave shaper or filter network in the receiving circuit of the fuze the associated amplifier can be peaked for maximum response to a definite behavior of change of phase or within upper and lower limits of such change. A predetermined behavior of phase change matching the shaping of the amplifier, for a fuze of given velocity and directional sen-; sitivity, will determine the relative position or aspect with respect to the target at which the fuze will be detonated,

assuming that the target is sufiiciently close to produce.

the proper amplitude of signal. It is clear that theamplifier can be designed to cause explosion of the projectile.

at a predetermined aspect and distance with respect to the target.

We have dealt in the foregoing with proximity fuzesfor use particularly against aircraft. An equally important use is the application for bombs to cause function at a predetermined height above ground. Against certain a bomb is tremendously increased if such function is obtained.

The fuze for this application is very similar to the fuze for use against a point target, such as an airplane, but design details are somewhat different because of the difference in the type of a signal, the difference in the attitude of the projectile with respect to the target, and the diiference in absolute sensitivity because of the particular range of operating heights needed for most effective operation.

The type of signal is different because the projectile can not pass the target as in the case of the airplane, but must approach it directly. The vertical velocity increases continuously until impact, except for the special case where terminal velocity of the bomb is reached. The rate of phase change of the detected pulses is proportional to the vertical velocity. The amplitude of the pulses varies inversely as the distance from the projectile to the ground surface.

In considering the design of a radio fuze for ground approach, knowledge. of conditions of use is important. The bomb, will be used from a certain range of altitudes,

and from airplanes flying in a certain range of speeds.-

These two factors will control the aspect of the projectile with respect to the ground, usually considered as a plane surface. Because of the different directional fuze-sen' sitivity characteristics feasible, aspect of the projectile withrespect to the ground surface controls the amplitude of the pulses. In the useful altitude range of from three thousand to about thirty thousand feet, with airplane speeds of from two to three hundred miles per hour, the bomb approaches the ground plane at angles varying from about 45 degrees to about degrees, angles being measured with respect to the vertical. It is obvious that if a uniform function height is desired, it is advisable to use an. amplier whose response to different rates of phase change compensates for the effect of the approach angle or sensitivity. Such compensation is practicable for an average speed of the bombing airplane, since the approach angle is then asimple function of the vertical velocity.

The best antenna for the purpose is a dipole disposed at right angles to the major axis of the bomb. As the bombs aspect approaches the vertical, the directional sensitivity is maximum. When the approach angle is 45 the directional sensitivity is reduced only by one half.

We have constructed fuzes utilizing antennas of this type which have functioned satisfactorily. There is, however, considerable difficulty in this design because of the mechanical stresses and vibrations introduced in the transverse antenna at air velocities of the order of 1000 feet per second. For this reason it is sometimes preferable to use an antenna whose sensitivity characteristics are less satisfactory, but whose mechanical characteristics are better. This arrangement is similar to that used in the fuze for use against aircraft in that the body of the bomb or projectile is used as the antenna. As has been pointed out, directional sensitivity is a minimum directly off the nose of the projectile and a maximum nearly ground targets the effectiveness,.or destructive power, of i ninety degrees off the projectile nose. Where angles with respect to the vertical are small, as in drops from high altitudes, the vertical velocity (and hence, rate of phase change) is high, and the directional sensitivity is low. Where angles with respect to the vertical are large, as in drops from low altitudes, the vertical velocity (and again rate of phase change) is lower, and the directional sensitivity is higher. The amplier is adjusted so that for high vertical velocities Where the directional sensitivity is low, the amplifier gain is high, while for low vertical velocity where the directional sensitivity is high the amplifier gain is low. This results in automatic compensation for the changing directional sensitivity as the angle of approach of the projectile to ground is varied.

' We believe that the above described methods including the use of predetermined directional sensitivities and the utilization of phase behavior in cooperation with controlled amplification of signals, to be entirely novel and we have found that the application of such methods to radio fuzes has produced results of remarkable reliability and accuracy.

A further object of our invention is to introduce a novel, electrically stable, fuze radiating and detecting circuit whereby optimum performance is obtained with manufacturing techniques adaptable to mass production methods. The novel feature of this circuit will become apparent from the following illustration: Device (I), referred to previously, could be converted into a fuze of the nature disclosed herein, through the addition of the dynamic amplifying means which forms a portion of our invention. However, in device (1), the reflected energy is made to react upon the oscillator to affect its operating parameters, thereby producing a change (as, for example, change in plate current) which bears some relation to the reflected energy. The sensitivity or response of this arrangement may therefore be said to depend on the parameters of the vacuum tube used as an oscillator.

In our device, every effort is made to eliminate this reactive elfect. We wish to make the energy source (i. e., the oscillator) as nearly as possible a constant voltage device. The coupling between the energy source and antenna circuit is kept well below the value generally known as critical coupling (the coupling for maximum power transfer). By this means, the reflected energy is largely contained by the antenna circuit, and is not returned to the oscillator. Under these conditions, the voltage developed in the antenna circuit is proportional to the voltage due to the energy of the oscillator and the reflected energy. The changes in this voltage are not influenced by the oscillator, and thus may be said to be proportional to the circuit parameters as determined by the inductance, capacity, and resistance of the antenna circuit hence by the energy reflected from the target. This dependence on circuit parameters instead of tube parameters is a major advantage, because the performance with regard to stability and sensitivity is independent of oscillator characteristics and gives greater uniformity and .reliability in production. Our experiments both in the laboratory and in the field have demonstrated superior qualities both with respect to stability and uniformity of performance. Manufacturing experience has also borne out these desirable qualities.

Another object is to provide a radio fuze that will not be appreciably affected by noise voltages, by changes in temperature and humidity, or by rough handling.

A further object is the provision of a radio fuze with safety features so that it will not cause an explosion while handling or while firing the projectile.

An additional object is the provision of a radio fuze suitable for use in a rocket or other type of projectile and which fuze will be capable of withstanding rapid acceleration and vibrations encountered in such use, with out injury.

An additional object is to arrange the fuze so that it will automatically cause in'l rv I "Another object is to provide a radio fuze that can be easily and quickly assembled from unit parts.

A'further object is to provide a method of firing a projec tile fuze with the use of electromagnetic radiation, which is positive and reliable.

A still further object is to provide a radio responsive device with a diode in the radiating circuit, the diode acting to measure changes in voltage due to the reaction of reflected radiation.

Other objects are the provision of a radio responsive device of general utility, the broad principles of which may be employed to make efiective burglaralarms, proximity indicators for airplanes flying relative to obstacles such as mountains or relative to other aircraft, and a device to indicate distance to ground for blind landings. It is contemplated that such a device could be used also by military or other vehiclestraveling in darkness to warn of the proximity of another vehicle or other object. Boats could also use the device for darkness or fog, to indicate the nearness of another boat or of land or any other object which would reflect the radio waves. Care would, of course, have to be taken to eliminate interference from ground reflections or reflections from the sea, as" the case may be. This could'be done by properly directing the radiation, or by suitable shields for the received radiation.

These and other objects of the invention may be better understood by reference to the accompanying drawings and the following detailed description. In the drawings-- IFig. 1 is a longitudinal sectional view of one form of the new fuze;

Fig. 2 is a perspective view of the fuze illustrated in Fig. 1, showing the oscillator nose separated from the amplifier ring;-

Fig. 3 is a view in front elevation showing a control switch of the fuze;

Fig. 4 is a detail perspective view of part of the amplifier unit;

Figs. 5 and 6 are sectional views on the lines 5-5 and 6-6, respectively, in Fig. 1;

-Fig. 7 is a perspective view of part of the amplifier adapter, showing the cellular construction and the manner of mounting the resistance and condenser units;

Figs. 8 and 9 are sectional views on the lines 8-8 and 99, respectively, in Fig. 1;

Fig. 10 is a schematic view of the wave pattern of the fuze;

Fig. 11 is a wiring diagram of the electrical circuits in the fuze, and

Figs. 12, 13 and 14 are diagrammatic views illustrating the effects of a shaped amplifier in the fuze.

Referring to the drawings, the radio fuze, as shown in Fig. 1, comprises an assembly of four sections A, B, C, and D which contain, respectively, the radio transmitterreceiver combination, the batteries and firing condenser, the set-back or timing switch and detonator, and the booster charge. A metal can 21 envelops sections B, C and D and is fastened to section A by means of a threaded ring 22 which is screwed onto threads 23 cut around a circumferential portion of a stepped metallic ring 24. The ring 24 also carries circumferential threads 25 at a greater diameter so that the fuze may be screwed into a suitable explosive projectile P, such as a bomb or rocket, containing an explosive charge E in which the fuze is embedded. The threaded ring 22 is welded or otherwise fastened to can 21.

The ring 24 is internally threaded at its front end as shown at 27, to receive a threaded metal ring 28 screwed against a shoulder 29. Secured to the ring 28 is a metal plate 30 which serves as a ground plate for high frequency currents and as 'an electrostatic shield between the oscillator and amplifier compartments. Also, the plate 30 serves as a support for a circular oscillator block its .own destruction after a cerably in the form of a hollow boss on block 31.

screw 42 may be screwed into cylinder 41 to press 31 made of Bakelite or othei' insulating material. l lat- 30 may be welded or dthe'rwise fasteiied to riiig 28, and the block 31 may be screwed to plate 30 or attached in any suitable manner. The plate 30 has siiitablopenings' for wires connecting the oscillator and amplifier circuits.

A tapered ring 32, which is a figure of revolution made i of phenol resin or other insulating material, has a boss 33 screwed into the threads 27 of ring 24 until an external shoulder of ring 32 abuts against the front end of ring 24, as shown at'34. A metal nose cap 36 has a threaded boss 37 screwed into the front end of ring 32, the external surfaces of the nose cap and the rings 24, 32 forming a streamline shape, as shown. While a threaded nose cap is shown, the cap may consist of thin metal cemented to an insulating extension of ring 32, or the metal may be plated or otherwise deposited on a nose piece of insulating material.

A metal cylinder 38 is mounted in the central portion of oscillator block 31 and forms the stator of a variable condenser C the movable element ofwhich comprises a metal rod 39 integral with a larger threaded rod 40. The rod 40 is screwed into a counter-bored cylinder 41 and a threaded opening in plate 30, to which cylinder 41 is welded or otherwise fastened. The inner surface of stator 38 is covered with insulating material, prefer- A set against the head of rod 40 and lock it in any position in which it has been set by means of a screw driver. The

i condenser stator 38 is electrically connected to metal cap 36 by means of soft copper wire 43 which is preferably soldered to both the stator and the cap, the latter having only its central portion connected to the wire.

A triode 44 is embedded in a potting compound in a ;metal shield 45 which is secured in an opening in plate 30 (Fig. 9), part of the tube 44 projecting into an opening 46 in oscillator block 31. A similar tube shield 47 extends from the opposite face of plate 30 and houses a pentode 48. The various tubes and associated elements are so placed that there is a minimum of interference or stray coupling between them, although the particular arrangement of the various parts may be varied widely. It is important, however, to shield the pentode amplifier circuit and the thyratron circuit, to be described, from high frequency currents to prevent theintroduction of noise voltages.

It will be seen that the tube shield 45 places tube 44 electrically in the forward or oscillator compartment in front of plate 30, and, similarly, the tube shield 47 places pentode 48 electrically to the rear of plate 30 or in the amplifier compartment. A thyratron 49 is supported in any suitable manner in the amplifier compartment and need not be shielded. The tube 49 may be separate from plate 30, if desired, and may be supported by its connec-v tions, together with potting wax.

A diode 5i) and a shield 51 for the diode are mounted in plate 30 in a manner similar to tube 44 and shield 45, so that the diode 50 is electrically in the forward or oscillator compartment.

The wiring for the oscillator parts is shown in Fig. 2, the parts being numbered to correspond to the general wiring diagram of Fig. 11. The oscillator parts are placed in openings or recesses in the insulating block 31 and are fastened in place with a suitable insulating cement of low dielectric loss, such as polystyrene cement or the like.

The amplifier is assembled on an insulating subchassis 52 somewhat similar to block 31 and is placed in the is important that all metal contacts be firmly connected. The potting material 52b also serves to protect the electrical parts from moisture. The amplifier connections are shown in Fig. 11. The amplifier may, of course, be wired in the compartment without a subassembly, but the latter is more convenient.

After all the connections are made and the potting material is poured in, care being taken not to seal up the condenser adjusting screw 40, a circular insulating plate 53 of Bakelite, or the like, is fastened to the rear face of ring 24, as by means of screws 53a. The plate 53 carries plugs 54, 55,, 56, 57, 58, 59 and 60, as shown in Figs. 1 and 4, which also show eyelets M and N for test purposes, and rim notches 61 for turning ring 24 with a spanner wrench. The connections to the various plugs and eyelets are shown in the wiring diagram, Fig. 11.

A central opening is preferably provided in the plate 53 so that the condenser adjusting screw 40 may be turned to vary the capacity of condenser C after removing locking screw 42. After final adjustment, locking screw 42 is replaced and the opening in plate 53 may be sealed to prevent tampering.

A cylindrical housing 63 having a removable end cap 64 is placed with its front face pressing against a resilient annular ring 65 which may be made of rubber or synthetic material. The ring 65 serves to maintain pres sure between the fuze sections B, C and D. The housing 63 contains A and B batteries and a condenser for firing the detonator. The batteries and condenser are arranged as illustrated in Fig. 5, which shows a condenser C of cylindrical form placed axially in housing 63. The housing 63 also contains the A battery 67 and the B battery, the latter being made up of a plurality of cylindrical multi-layer units 68 in series. The A and B batteries 67, 68 and a C battery 69 are disposed around the condenser C as shown. The terminals of the batteries and condenser are connected with seven sockets 54, 55, etc. (Figs. 1 and 11), fastened in the face 70 of the battery case and arranged to receive the plug 54, 55, etc., shown in Fig. 4.

The end cap 64 of the battery case has sockets 71, 72', 73', 74, 75' and 76' adapted to receive plugs 71, 72, 73, 74, 75 and 76, respectively, arranged as shown in Fig. 3 and connected with a set-back switch 77 and with a detonator 78. The detonator is placed in a central opening 79 in switch 77 and is adapted to fire a powder train leading to the tetryl in chamber D, through a passage 80 formed by a central opening in a threaded cover plate 81 for a cylindrical switch housing 82 and by an aligned opening in the tetryl container 83 which has a flanged cover 84 clamped against it by a spun rim 85 on the can 21. The housing 82 contains the set-back switch 77 which comprises a slide 86 having an opening 87 and suitable rack teeth meshing with a gear 87a. The slide 86 is normally positioned as shown to block the entrance to passage 80, so that the tetryl will not be fired even if detonator 78 is set olT prematurely. When the switch is given rapid acceleration, however, as in firing the projectile P, a small weight (not shown) acts by its inertia to release the switch mechanism so that gear 87a is driven by a spring (not shown) and moves slide 86 downward until opening 87 registers with passage 80. At the same time, spring operated contacts 88 and 89 (Fig. 11) in the switch are released to close the battery circuits within approximately 0.08 second after the initiation of set-back, thereby energizing the electrical circuit. Approximately 0.40 second later metal cap 90 on slide 86 is brought down to touch contacts 91 and 92, the bridging of which connects electrical detonator 78 into the plate circuit of the thyratron 49. The arming of the device, therefore, requires approximately half a second, although the timing may be chosen as desired. The time delay is incorporated as a safety feature and also to minimize the effect of transient voltages which appear across the thyratron grid circuit during the warming-up of the filaments of (ill the radio tubes. The set-back-operated timing switch C per se forms no part of the present invention, and a suitable form of the switch is disclosed in a copending application of W. B. McLean, Ser. No. 565,782, filed November 29, 1944.

In order to insulate the sockets and to prevent stray currents, the battery casing, including end cap 64 and end face 70, is preferably made of Bakelite or other insulating material. In any event, the sockets are insulated one from the other.

Set-back switch C is illustrated diagrammatically in Fig. 11 which shows switches 88 and 89 representing the A and B battery switches, respectively, the switches 88 and 89 being spring-operated in switch C to close within 0.08 second, as described] above. Switch 91-92 in Fig. 11 represents contacts 91 and 92 which are bridged by cap 90. Plugs 71, 72, 73, -74, 75 and 76 of set-back switch 77 are mounted in an insulatingplate 82a attached to housing 82 and are brought into contact with corresponding sockets 71, 72'', 73?, 74', 75" and 76 in the battery cap 64 as shown, the connections of the socketsbeing also illustrated in the diagram of Fig. 11. It will be observed that the connections for the set-back switch and detonator are shown to the left of line CC in Fig. 11; the connections for the batteries and firing condenser C are included. between lines CC and B-B; the connections for the amplifier and thyratron are shown between lines B--B and A-A; and the connections for the oscillator and diode are shown to the right of line AA.

T he rim of cup 83 is preferably welded or brazed to the inside surface of can.2'1. to render the can moisture-proof. The cup is then filled with tetryl and closure 84 is secured bycrirnping or spinning the rim 85, or the tetryl could be inserted afterwards through the opening in cup 83. This construction allows the can 21 and the tetryl chamber D to be shipped as a separate unit, as well as sections A, B, and C respectively. The complete fuze can be readily assembled by first placing set-back switch C in can 21 and then placingbattery and condenser section B in the position shown. Then section A is attached by screwing ring 24 into ring 22 which is fastened to can 21 in amoisture-proof manner. As previously described, resilient gasket causes the various sections to be firmly pressed together to make good contact. The threads of rings 22 and 24 and of cap 36 areadapted to form moisture-proof connections;

The wiring diagram of Fig. 11 shows the electrical connections of the various tubes, plugs, sockets, batteries, condensers, inductances, resistances, switches, detonator, and the cap 36. Although the diagram is largely selfexplanatory, the various elements of the circuit previously mentioned will be briefly described. The ground, as

shown, represents metal plate 30, ring 24, can 21, and

second. The unloaded diode: voltage is the diode voltage obtained when there is no radiating or dummy load on the diode circuit. The projectile, for this test, should be under substantially free space conditions equivalent to being supported 15 feet above ground in a clear field.

Referring to the oscillator circuit. (Figs. 8 and 11),

C is the variable condenser and L is the antenna coupling and diode coil coupled to inductance L which is the oscillator plate coil. L also provides a D. C. path between cap 36 and ground, which is the body of the vehicle, to prevent. the accumulation of static charges on the cap. These charges, if not removed, mightcause preessas se mature functioning of the fuze. C is the diode coupling resistor, R the diode coupling resistor, and R the diode load resistor. L is the oscillator plate supply choke, L the oscillator grid coil, C the grid return condenser, C the plate return condenser and C the triode filament bypass. R is the blocking resistor for the oscillator grid, used for test only, and R is the oscillator grid leak.

With reference to the amplifier and thyratron circuits (Figs. 6 and 11), C is an R. F. by-pass for the diode output, C a coupling condenser, C an R. F. by-pass for the pentode grid, C an R. F. by-pass for the pentode filament, C an audio by-pass for the screen grid, R; a grid bias resistor, R, a blocking resistor for the feed back circuit, R the feed resistor for the screen grid, R a load circuit resistor for the positive B battery terminal for dis charge of various condensers when the B battery voltage is removed, and L is an R. F. choke to keep radio frequency current out of the pentode.

Resistances R R R R and condensers C C C constitute a phasing and feedback network to provide regeneration and high frequency cut-off for the amplifier. It is desirable that the amplification-frequency characteristic be so shaped that amplification at frequencies greater than a predetermined maximum or lower than a predetermined minimum shall be a fraction of the amplification occurring within the chosen limiting frequencies. As an illustration, we have found that, in the case of our rocket radio fuze, the amplification for frequencies greater than 300 cycles/sec. and lower than 25 cycles/sec. should be not more than 25 percent of the peak amplification. In this case, it is preferable that the frequency of peak amplification shall be between 95 and 155 cycles per second. The above-mentioned phasing and feed back network acts as a wave shaper to limit the amplification as described.

The tubes used in the fuze are of small size and preferably require a 1.35 volt A battery 67 for the filament and a 135 volt B battery 68. The diode is used as a peak voltmeter and detector at frequencies up to 155 megacycles per second or more. The thyratron should be fired when the voltage input to the amplifier is not more than 0.050..

volt R. M. S. but should not be fired when the voltage input is less than 0.025 volt R. M. S. The maximum allowable peak self-noise voltage appearing between the thyratron grid and ground should be not more than 0.400 volt. This self-noise voltage can be measured with a cathode ray oscilloscope or equivalent device. The warmup transient voltage appearing between the thyratron grid and ground should be reduced to less than 0.5 volt peak,

- within 0.40 second after applying plate and filament voltpulse to the thyratron grid through timing resistances R and R so that the thyratron will conduct after a predetermined time interval, preferably from 6 to 12 seconds,

with the result that the detonator will be fired after that I interval in case the reflected radiation is lacking or is insuifi'cient to cause an explosion of the device. Neon tube 66 preferably has a breakdown voltage of 70 to 80 volts. The neon tube condenser C is charged through resistance R until the breakdown voltage is reached, at which instant tube 66 passes current so that a potential difference is placed across resistance R 'to apply positive voltage to the thyratron grid, thereby firing'the detonator 78.

L is an R. F. choke placed in the set-back switch compartment C to minimize the eflects of an arming pulse. R is a filament resistor and R is a plate resistance for the thyratron, connected as shown. The B battery 611A battery 67, C battery 69, and detonator 78 are connected into the circuit in the manner illustrated in Fig. 11. As'

pointed out heretofore, the A battery switch 88Iand the B battery switch 89 are operated by set-back to close when the device is fired.

All parts should be fastened tightly in place andthe various units should be firmly pressed together so that there will be no rattling or intermittent contacts to generate noise voltages.

The operation of the device depends upon a phase behavior principle as described, the change of behavior being generated as a result of relative movement between the fuze in flight and another object such as an airplane. In Fig. 11, the oscillator inductance L and the diode coil L are rather loosely coupled so that variations of antenna current or voltage will not react upon the oscillator appreciably. The diode acts as as antenna voltage measuring device or as a rectifier for currents in the diode resulting from the interaction between the pulsations induced in the diode circuit by the oscillator and the reflected radiation which is returned from the airplane or other object and is received by the antenna system in-' cluding cap 36 and the connected fuze and projectile .body, which together may be considered as a dipole. This modified dipole also acts as the transmitting antenna system, and therefore the previously described energy pulse,

resulting from the phase and amplitude difference of the transmitted and reflected energy, is developed in the diode circuit. The shape of the pulse depends in part upon the rate of relative movement of the transmitting antenna system with respect to the reflecting airplane or other object.

If now the radiating system is given relatively rapid phase of the transmitting antenna current, and this phase change produces voltage variations which, through coupling resistor R and coupling condenser C will be fed into the grid circuit of amplifier tube 48 and thence to the thyratron 49. As previously mentioned, the wave shaper or cut-off network passes only pulsations of the desired phase behavior for the particular radio fuze under consideration. Pulses, the amplitudes of which vary with time at rates substantially greater or less than the rate determined by the wave shaper, are rejected.

As the radio fuze approaches closer to the airplane, the

By aspect is meant the relative position of the fuze with respect to the target, when the projectile does not approach it directly but passes near it. In this connection it is important to consider the radiation and sensitivity patterns of the fuzed projectile. Curves showing various radiation and sensitivity patterns are illustrated in Fig. 10. The projectile P, carrying a radio fuze, is assumed to be traveling in a straight line at uniform velocity V in the general direction of airplane Z. If V, is the velocity of the fragments of the rocket projectile, in a The fragments would actually fly radially out from the Q 1 1 rocket or other projectile in a more or less uniform pattern around the circumference.

Curves L and'Wrepresent, respectively, the approximate field sensitivity pattern and the signal phase behavior and intensity, under the simplified assumption that (a) the field intensity varies with distance according to the inverse first power law, i. e., the target acts as reflector and not as a reradiator; (.b) that the velocity of the projectile is constant; (c) that there is no time delay between the time the signal is of sufiicient intensity to fire the charge and the time the fragments start flying. It is also assumed that the plane target, for instance, is a point target and acts as a perfect reflector. In this case the coefficient. of reflection is 1 and the intensity of the signal refiectedis proportional to /2r where r is the distance of the transmitter to the reflector.

As the projectile approaches the target from a distance, along line T, it will be seen that the velocity toward the target becomes progressively less until it reduces to zero relative velocity when it passes the target, there being no change of distance with respect to time, at this point. The phase behavior of the signal, which is dependent upon relative velocity, therefore continually changes as the target is approached, and the intensity of the signal constantly increases as the projectile comes nearer the reflecting plane Z. This condition is represented by curve W which indicates cycles of phase behavior and also intensity of signal, as measured from line T. The. envelope of peak signal intensities is represented by curve W. Curve W represents the envelope of signal intensities when the amplifier is shaped. Reference to Figs. 12, 13 and 14 illustrate further the effects of a shaped amplifier.

The normal radiation pattern is shown'by curve Lin Fig. and its median plane is inclined slightly rearward from a vertical plane through the projectile. This curve presupposes a perfect spherical reflector and a fiat amplifier.

Curve N shows the sensitivity pattern with the effect of the shaped amplifier included and assuming also a perfect reflector and uniform velocity.

Curve M represents the estimated actual signal sensitivity pattern which results from a modification of curve N due to the effect of time lag in the amplifier. It will be observed that this final pattern has a forward tilt so that the pattern, which might also be considered a locus of firing points, intersects airplane Z before the projectile P reaches a vertical plane, passing through the target. In this way the firing operation is begun when the projectile is approaching the target at a sufificient distance to allow time for functioning of the firing means as well as for the fragments to reach the target along resultant path R.

By means of such predetermined sensitivity patterns it is possible to regulate the explosion of a projectile, with relation to a target, for maximum destructive effect. The special amplifier thus plays an important part in regulating the distance of firing since the phase behavior is constantly changing as the target is approached and the amplifier can be designed to correspond to any desired aspect, assuming, of course, that there is suflicientsignal intensity at that point to cause firing.

If the projectile approaches the target directly, as in the case of a direct hit, the rate of change of phase would be constant for a point reflector, assuming uniform speed of the projectile. In practice, however, there will be refie'ctions from separated areas such as the wing tips or tail surfaces of an airplane, for instance, so that there will be change of phase behavior as explained previously. It will be noted however that the sensitivity pattern shows small intensity directly forward so that under the condition of direct approach, the signal intensity will not be sufficient to fire the fuze until it is almost at the target. In this way premature detonation resulting in effective scattering of fragments is avoided.

The shapes of radiation or sensitivity patterns can be predetermined by relating the frequency of the carrier 12 emitted from the fuzed projectile to the length of the projectile- In the various, fuze models which we have designed and. tested, the specifications for. performance havebeen such that the signal from the various antenna systems was far less than thevalue with which it is practicable to operate. the control and detonation components, which appear in this. disclosure- Also in certain cases these performance specifications required a particular type of operation, such as the requirement that a particular type fuze shall not operate until it commences to pass the reflecting object. A. requirementfor. another type fuze is that the fuzeshall. function when itsmotion with respect to a predetermined object is at arate which is not less than, nor in excess of, certain specified limits. A. general requirement for all fuzes is that they shall not respond to signals which.

are not. within the particular limits; that is, limits of. phase behavior which correspond to the limits for the velocity, or rate of motion. This latter requirement is due to the necessity for assuring that the fuze will not function on other spurious signals; as for example, those which may be generated through accidental mechanical vibrations or resonances.

In order to explain how the foregoing is accomplished,

- .must. function on passing within 60 feet of a metal airplane, anditmust not function until it commences to pass that airplane. With respect to a circular plane area, the

center of which is the center of. the airplane, and which is perpendicular to the trajectory of the projectile, the

. fuze must function when an angle defined by the fuze, the

center of the circular area, and the area itself is about,30 degrees, the point offunction being before the fuze passes through the plane.

From this specification, it is desirable that the emitted energy be directed sothat maximum power, and hence, maximum reflected signal, is directed nearly at right angles to the trajectory of the projectile. sirable that the amplifier be unresponsive to the phase behavior of such signals as are produced by direct approach to the airplane, and responsive only to the phase behavior of signals which are produced when the projectile commences to pass the airplane. The first feature is accomplished automatically by utilizing the body of the projectile as a simple antenna, and exciting it with power of such a radio frequency that the antenna is resonant at about /2 wave length. The sensitivity pattern (radiation pattern squared) of such a system is shown in Fig. 10. Having determined the radio frequency at which the fuze will operate as a transmitter, we may then determine the mode of phase behavior and amplitude of signal at which we wish to operate the fuze to satisfy the second feature. The mode of phase behavior and amplitude are dependent on the radio frequency of the emitted wave, and on the relative velocity of the fuze with respect to the airplane and the distance therefrom.

The relative velocity is equal to the projectile velocity times the cosine of the angle defined by the position of the reflecting object with respect to the projectile and the trajectory of the projectile. Thus, as previously stated, the relative velocity changes from the full projectile velocity on direct approach, to zero relative velocity at the nearest point of passage, or when the reflecting object is exactly at right angles to the trajectory of the fuze and projectile.

Early in our experimental work leading to the production of effective radio fuzes it became evident that, without electrical stability under conditions of severe shock and vibration, a fuze of this nature could not be made to operate satisfactorily. By stability we mean that spurious signals, sufiicient to cause the fuze to function prematurely before it reaches the target, are not gen- It is also de- 13 erated within the fuze proper. The means by which this stability is obtained are therefor primary considerations in fuze design. These means may be classified (1) .oscilfore developed the design principles illustrated in Fig. 1

and associated figures. The essential feature is that every element, including the connecting wires, is fastened rigidly, as with cement, to a secure mounting, in this case to heavy insulators which are in turn rigidly fastened to a strong metal base.

The electrical circuit design is also part of the design for stability. We have found that stability of the circuit arrangement with respect to electrical design, which is part of our invention, is superior to that of different arrangements which we have tested or of which we have knowledge.

We have described the means by which spurious and undesirable noise pulses are held to a minimum. Even though all these precautions have been included in the most satisfactory manner, it is desirable and necessary to restrict the fuze operation so that it is responsive only to such signals as are useful in its proper operation. By the means previously described of providing rigid mountings for all components, we reduce spurious noise pulses i and further assure that such noise pulses as remain will be at a relatively high rate of occurrence (greater than 1000 persecond) as compared to the signals which are used in obtaining fuze operation. These signals correspond to rates of occurrence in the band 50 to 300 per second, approximately. Thus it is evident that a band pass amplifier which accepts signals in the useful band up to about 300 per second, and which rejects signals having rates of occurrence above that band is useful and as we have found necessary in the design of a satisfactory radio fuze.

In referring to rate of occurrence .of the signal above, we mean considered in the light of phase change'since, as in the case of an airplane target, the rate of occurrence of signal continually changes. In the case of a falling bomb equipped with a radio fuze there would be a true signal frequency if the bomb shall have reached its limiting velocity while receiving reflected radiation from a target.

Our radio fuze is particularly adapted for use with a rocket projectile but is not limited to that use. Such a rocket is especially desirable for discharge from an airplane since the reaction on the aircraft will be negligible as compared to the shock of firing a gun of comparable caliber. Radio rockets of this type can be fired at another airplane with the result that the rocket explosive charge will be automatically detonated to destroy the enemy aircraft when the rocket bearing the radio fuze passes within a certain effective distance from it. This provides a very effective means for attacking and destroying enemy aircraft. It is contemplated that this radio fuze can also be used with shells.

While our radio fuze is called a proximity fuze its operation is not dependent upon merely its spatial relation to other objects, as has been clearly shown. Its demonstrated effectiveness depends among other things upon the principle of employing electrical effects resulting from relative movement between the radio fuze and the reflecting object whether it be an airplane or other target. Since actual relative movement is required in order to detonate the device, it is less susceptible to capacity effects or to static charges or other disturbing influences than would be the case if it operated merely upon the basis of reflections from a relatively stationary object; This feature then, in cooperation with predeter-j mined radiation and sensitivity patterns and shaped amplifier makes possible the design and construction of' a'more stable, a safer, and more reliable device in general than otherwise would be the case.

We have shown and described a practicable radio fuze. We contemplate however, that a wide variety of other devices, both military and commercial, and employing the general principles underlying our device, can

be made. Some of these possibilities have already been mentioned.

Bombs have been equipped with the radio fuze so as to explode before reaching ground, to scatter shrapnel,

incendiaries or other missiles downward upon troops, ships, airplanes, grounded or flying, or upon any other object of attack.

We have outlined a few possible applications of the general principles inherent in our device but we are aware .that many other variations and adaptations can be made without departing from the broad aspects of our invention.

The invention herein described may be manufactured and used by or for the Government of the United States of America for governmental purposes without the pay- 'ment of any royalties thereon or therefor.

We claim:

1. In combination, an antenna adapted to radiate electromagnetic energy and to receive part of said energy returned bya reflecting means, an oscillator coupled to the antenna for radiating electromagnetic energy therefrom,

a diode detector electrically connected with the antenna for producing a signal correlative with the difference in frequency between radiated and received energy, an am- .plifier coupled to said diode detector, a detonator, and a 'relay connected with the amplifier for controlling operation of the detonator.

2. In a radio fuze for explosive projectiles and the like, an antenna acting both as a radiator and receiver of electromagnetic energy, an oscillator coupled to the an- "tenna and having an inductance, a diode coupled to the 3. In a radio fuze for explosive projectiles and the like, a housing including an antenna acting both as a radiator and receiver of electromagnetic energy, a chassis in the housing and insulated therefrom, an oscillator coupled to the antenna and including oscillator elements mounted on the chassis, a diode coupled to the antenna and having diode elements mounted on the chassis including an inductance loosely coupled to the oscillator, a second chassis in the housing spaced from the first chassis and insulated from the housing, an amplifier coupled to the diode and including amplifier elements mounted on said second chassis, a thyratron coupled to the amplifier and mounted in the housing in the space between said chassis, and an electrical detonator operable through the thyratron.

4. In a projectile carrying a radio proximity fuze, means for radiating electromagnetic energy, an oscillator loosely coupled to said radiating means, said radiating means acting partly also to receive some of said energy reflected from a target, diode rectifying means coupled to said radiating means for causing interaction of said radiated and received energy to produce a signal having a rate of change of phase between upper and lower limits with respect to a reference, filtering means for selecting only signals having rates of change of phase between the said limits, an amplifier for said signals, a detonator, and a relay for controlling current to said detonator and operated by current from said amplifier.

5. In a projectile carrying a radio proximity fuze,

1 5 means for radiating electromagnetic energy including an antenna circuit, said antenna circuit acting partly also to receive some of said energy reflected from a target, a diode detector for producing a signal resulting from interaction of said radiated and received energy and correlative in frequency with projectile target velocity, means for amplifying said signal, a relay electrically coupled to said amplifying means, and a detonator controlled by said relay.

6. In a projectile carrying a radio proximity fuze, means for radiating electromagnetic energy including an antenna circuit, said antenna circuit acting, partly also to receive some of said energy reflected from a target, a diode detector in said antenna circuit for producing a signal resulting from interaction of said radiated and received energy and correlative in frequency with the projectile target velocity, means for amplifying said signal, a relay electrically coupled to said amplifying means, and a detonator controlled by said relay.

7. In a projectile carrying a radio proximity fuze, means for radiating electromagnetic energy including an antenna circuit, said antenna circuit acting partly also to receive some of said energy reflected from a target, a diode detector for producing a signal resulting from interaction of said radiated and received energy and having a rate of change of phase correlative with the projectile-target velocity, means for amplifying said signal, a filter for passing said signal from said diode detector to said amplifying means only when the signal has a rate of change of phase within predetermined limits, a relay electrically coupled to said amplifying means, and a detonator controlled by said relay. 1

8. In a projectile carrying a radio proximity fuze, means for radiating electromagnetic energy including an antenna circuit, said antenna circuit acting partly also to receive some of said energy reflected from a target, a detector for producing a signal resulting from interaction of said radiated and received energy and having a rate of change of phase correlative with the projectile-target velocity, means for amplifying said signal, a phasing and feedback network connected to said amplifying means for varying the amplification characteristics thereof correlative tothe rate of change of phase of said signal, a relay electrically coupled to said amplifying means, and a detonator controlled by said relay.

9. In a projectile having a radio proximity fuze, means for radiating electromagnetic energy of a response pattern which is inclined forwardly from a plane throughthe projectile and normal to the axis of the projectile; said means acting partly also to receive some of said energy reflected from a target, diode detecting means for producing a signal resulting from interaction of said radiated and received energy and having frequency characteristics correlative with. the projectile-target velocity, a, peaked amplifier for said signal, a relay electrically coupled to said amplifier, and a detonator controlled by the relay.

10. In a projectile carrying a radio fuze, means for radiatingelectromagnetic energy, said means acting partly also to receive some of said energy reflected from a target, diode rectifying means for producing a signal resulting from interaction of said radiated and received energy and having frequency characteristics correlative with the projectile target velocity, an amplifier for said signal, a relay electrically connected with said amplifier, anda detonator controlledby said relay.

11.. In a projectile incorporating a radio fuze, means for radiating electromagnetic energy of predetermined intensity pattern, said means acting partly also. to receive some of. said energy reflected from a target, diode detecting means for producing a signal resulting from interaction of said radiated and received energy and having frequency characteristics correlative with the projectiletarget velocity, a peaked amplifier for said signal, a relay electrically connected with said amplifier, and a detonator controlled by said relay, said amplifier passing said signal only when the frequency therof is Within a predetermined range of frequencies whereby the fuze is detonated only when a predetermined condition of proximity of the projectile and target exists.

References Cited in the file of this patent UNITED STATES PATENTS 2,022,517 Patterson Nov. 26, 1935 2,137,598 Vos Nov. 22, 1938 2,176,469 Moueix Oct. 17, 1939 2,205,881 Franz June 25, 1940 2,210,666 Herzog Aug. 6, 1940 2,255,245 Ferrel Sept. 9, 1941 2,403,567 Wales July 9, 1946 2,408,742 Eaton Oct. 8, 1946 FOREIGN PATENTS 546,488 Great Britain July 16, 1942 

